They're looking for participation from "anyone who has grown up speaking English in America or Canada". All you need is an internet-connected computer with a microphone and a web browser that can run Flash. You participate by connecting to a Flash application that gives you prompts and records your responses.

They ask for basic demographic information, but participants are of course anonymous. This is a great idea, and I certainly encourage participation. Check it out!

If you're an English speaker from outside North America, hang on, I expect that they (or others) will get to you soon.

@Marie-Lucie, there's been a lot of work done on US dialects too :) but somewhat to our surprise no one had done a large-scale standardized phonetic survey — Labov's Atlas of North American English is the largest, but it's based on 437 detailed analysis, which is a lot in phonetic transcription terms but not much when looking at correlates of variation on a national level. It's also only "white" speakers, so to my mind it doesn't give a proper picture of US dialectal diversity more generally. We looked at trying to mesh Labov's results with other surveys of regional varieties (for example the work that Erik Thomas and colleagues have been doing) but because each survey used different prompts it was hard to get enough coverage of comparable data.
@myl: Bardi has 23 phonemes and if I count right, 16 of them are written with digraphs in the "practical" orthography. Even I can't spell my email address aloud half the time.

Daniel Ezra Johnson said,

What exactly is a "large-scale, standardized phonetic survey"? Also, while the interface is certainly modern, this survey is nevertheless a short word list with one or two words per phoneme. How much can we say about an individual's phonetics (or phonology) based on this? And if the point is to make statements about groups of speakers, is the data from individuals even enough to normalize?

Jerry Friedman said,

I did the survey (MacBook, btw, so that's fine), but more importantly, I passed it along to friends and family—as someone with a linguistics background I was really fighting not to overthink it. :) Also was pleased to note that my first name—"Don"—was in there, as I've noticed that its vowel is a pretty significant dialect marker (I have a Chicago /a/ in there, but /ɑ/ and /ɔ/ are more common; some merge it with "Dawn" and some not, independently of which vowel is used although "Dawn" is always more back and/or more high; and to some hearers, when I say my name as /dan/ they hear /dæn/).